Method of and apparatus for winding a web of material

ABSTRACT

Apparatus for winding a web of material, such as plastic film, including a web tension feedback controller means operatively connected to all of the windup rolls mounted on a turret wherein all such windup rolls respond to a control signal from a web tension-sensing device, whether they are loaded or not. Method of winding a web while maintaining required web tension including controlling the speeds of loaded and next-to-be-loaded windup rolls mounted on a turret by means of a web tension-sensing device whereby the unloaded windup roll is driven at a speed greater than the speed of the loaded windup roll during transfer of the web from the loaded windup roll to the unloaded windup roll.

United States Patent METHOD OF AND APPARATUS FOR WINDING A WEB OF MATERIAL 4 Claims, 5 Drawing figs.

US. Cl 242/64, 318/7, 242/7551 Int. (1 B65h 75/34, B65h 59/38, B65h 77/00 Field of Search 242/64,

[56] References Cited UNITED STATES PATENTS 2,990,484 6/1961 Jones 310/94 3,283,228 11/1966 Asseo 242/75.51X 3,372,320 3/1968 Boyum et al 318/7 Primary Examiner-Leonard D. Christian Attorney-liege T. Sutherland ABSTRACT: Apparatus for winding a web of material, such as plastic film, including a web tension feedback controller means operatively connected to all of the windup rolls mounted on a turret wherein all such windup rolls respond to a control signal from a web tension-sensing device, whether they are loaded or not. Method of winding a web while maintaining required web tension including controlling the speeds of loaded and next-to-be-loaded windup rolls mounted on a turret by means of a web tension-sensing device whereby the unloaded windup roll is driven at a speed greater than the speed of the loaded windup roll during transfer of the web from the loaded windup roll to the unloaded windup roll.

POWER SOURCE FIELD clncun FIRST ARIATURE CIRCUIT PATENTEUFEBISISYI 3563485 v sum 1 or 3 FIG.

INVENTOR TERRANCE D. PHILLIPS BY dyf'faz f-ia ATTORNEY PATEN TED FEB 1 61971 'VIEB TENSION TENSION SENSING MECHANICAL To PNEUMATIC I AVERAGER T ENSION SIGNAL SHEET 2 BF 3 7 AIR ELECT v I Q nscu.

L ()ssr Pom STTIORT 8% I O 0 11 ISI w iRBuP znv IIlTwur ROLL ROLL FIG 4 TENSION READOIIT DESIRED TENSION COMPARED wnn SET POINT (CONTROLLER) LPNEUIIAT IC T0 ELECTRICAL CONTROL SIGNAL II I m TENSION FIRST mm ROLL l0 SET POINT SET BY OPERATOR I ELECTRIC POWER CONTROL NEGATIVE FEED BACK SECOND NINDUP ROLL INVENTOR TERRANCE D. PHILLIPS BY WE'SW ATTORNEY METHOD OF AND APPARATUS FOR WINDING A WEB OF MATERIAL BACKGROUND OF THE INVENTION A 1. Field of the Invention This invention is a web-winding method and apparatus including a constant tension control system for turret-type windup rolls for maintaining the requisite web tension and speed control during roll changeover. 1

2. Description of the Prior Art I In known devices or systems for'winding a web of material such as plastic film, onto a windup roll, there are four general or basic winding patterns: constant torque, tapered torque, constant tension, and tapered tension.

At constant torque, there is an associated rapid decrease in tension with increasing roll diameter; at tapered torque, the torque increase is a nearly linear change with revolutions per minute which produces an increase in tension followed by a decrease in tension during roll-buildup. With constant tension, the torque must increase proportionately to roll diameter; with tapered tension, the tension decreases with roll diameter and is achieved by modifying a constant tension torque pattfln.

US. Pat. No. 2,990,484 to Jones and US. Pat. No. 3,372,3 to Boyum etal. are exemplary of the prior art winding techniques. These patents show web winding devices having adjustable speed drives for-windup rolls, response to changes in windup roll speed during the winding operation whereby to maintainuniform tension on the webas it is wound.

All of techniques known to applicant in this area maintain proper tension on the web as his wound onto a loaded windup roll by controlling the speed of the loaded winduproll only;

' applicant, on the other hand, includes in his method and apparatus the inventive act or means of also predriving the nextto-be-used unloaded windup roll at a proper speed so that the web might immediately be wound onto this empty windup roll while maintaining the proper tension in the web during roll changeover. I

None of the known systems anticipates the need for maintaining, on an automatically controlled basis, the requisite web tension and speed of an empty unloaded second windup roll being placed into service after "the first windup roll has received a predetermined web load wound thereupon. All previous systems have required secondary or manually operated programmed speed systems to do this.

SUMMARY OF THE INVENTION The web-winding apparatus of this invention is substantially continuous and automatic in operation.

Specifically, the present invention is directed to improvements in webwinding apparatus including means for maintaining a constant tension on the web as it is wound onto successive windup rolls and a control system associated therewith. I

Briefly described, in such apparatus by imparting 'a predetermined speed to the next-to-be-used empty windup roll prior to its being made a part of the actual web winding operation or system (i.e., prior to winding the web onto this roll after the windup roll used before it is completely loaded), the desired tension on the web being wound is maintained even during the difficult web transferring or changeover operation. r I

It is important when winding a web of material into roll form onto a windup roll to avoid variationsin tension on the web during the winding operation in order to obtain a roll wherein the wound material is of uniform tension between the core of paratus having winding tension control means and while they bring about some improvement over apparatus without any tension control means, they fail to provide a satisfactory solution to the web-winding problem of maintaining proper web tension during changeover from a loaded windup roll to an empty windup roll.

The present invention provides web-winding apparatus having means for controlling these and other factors contributing to improper web tension, and, capable of winding wound rolls of web material characterized by uniform tension between the core of each roll and the outer peripheral edge thereof.

This invention solves the problems existent in the prior art by providing an improved method of controlling web-winding tension even during roll changeover by use of a novel con troller means which drives the empty windup roll at a speed higher than the speedof the loaded windup roll, such speed being based on or determined by the existing tension in the web at the time of transfer as relayed to the control means by a tension-sensing means or device as will be described in detail.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic representation of parts of a web winding apparatus of this invention;

FIGS. 2 and 3. are schematic representations of parts of the pneumatic-electrical system of the apparatus of the invention, some of the parts being shown in block form;

FIG. 4 is a block diagram of the web tension controlling system of this invention; and,

FIG. 5 is a schematic representation of the electrical control system of the apparatus of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT This invention is a web-winding apparatus including a web tension controller means operatively connected to both loaded and unloaded constant tension windup rolls mounted on a turret for controlling the speeds of these rolls during windup. I

In the practice of the invention, a loaded first windup roll 10 (the windup roll onto which a web W is currently being wound) and an unloaded second windup roll 20 (the windup roll onto which the same web W is next to be wound) are controlled by a web tension feedback controller means 30 which, acting in accordance with tension control signals from a tension-sensing device or means, drives both the loaded and unloaded windup rolls l0 and 20 at the proper and different speeds to effect or maintain proper tension in the web W at all times.

Briefly described, the web tension controller means 30 and associate parts guarantee that the second windup roll 20 running at no load will always be running faster than line speed of the web W by providing an applied armature voltage to a second motor M-Z driving the unloaded or empty second windup roll 20 higher than the applied armature voltage to a first motor M-l driving the loaded first windup roll 10 whereby to effect proper tension in the web W, particularly during web transfer.

The speed of a direct current '(DC) motor and, hence, the speed of the windup roll driven by it is directly proportional to the applied armature voltage. However, when winding a web at a constant tension with a DC motor drive, the magnitude of applied armature voltage supplied to the DC motor must be decreased, thus creating a slower potential winding speed, as the diameter of the web being wound onto the windup roll is increased, whereby the line speed of the web remains constant. Consequently, in order to simultaneously control both windup rolls and 20 (i.e., the one onto which the web W is being then wound and the empty roll onto which the web will next be wound) from a common tension feedback signal and guarantee that the unloaded second windup roll motor M-2 will travel fast enough to pick up the web W without slacking during a roll changeover, the applied armature voltage to the unloaded second windup roll motor M-2 must be greater than the applied annature voltage to the loaded first windup roll motor M-l. The control system of the present invention accomplishes this.

Referring to the drawing and FIG. 1 in particular, the web W of sheet material to be wound by the web winding apparatus of this invention is supplied from a supply source (not shown) and moved or advanced into operative association with means for controlling the tension on the web W as it is successively wound onto the first and second windup roll 10 and 20 and during web transfer from the first to the second windup roll in a manner to be described.

The supply source may be any appropriate source, such as a supply roll or may be a web of plastic film as it emerges from a polyolefin or polyester film production line, for example.

From the supply source, the web W passes under and over a plurality of rolls ll, l2, I3, 14 and 15 and onto a core or mandrel 16 of the first windup roll 10 appropriately mounted on a turret T.

Roll 11 is a driven roll and rolls 13, 14 and 15 are idler rolls and all of them are suitably and rotatably mounted on a frame means (not shown) in a manner known to the art.

Roll 12 is a tension idler roll and is rotatably secured to the outer ends of pivot arms 17, the other ends of which arms are pivotally mounted, as shown at [8, to the frame or support means. The tension roll 12 is, therefore, rotatably and movably mounted with respect to the frame, such motion being caused by or created by the tension in the web W at a given time.

Two force transmitters 19 are positioned adjacent roll 12. Web tension applies force to the tension roll 12 and the force is transmitted through the pivot points 18 (one shown of two), and applied to the two pneumatic force transmitters 19, one at each end of the tension idler roll 12.

Increased web tension results in increased air pressure from the force transmitters 19, as the web moves. The resultant tension signal 21 from a force averager 22 is indicated as film or web tension on an operators gauge 23, and applied as the process input to the web tension controller means 30, as best seen in FIGS. 2 and 3.

It is seen, therefore, that the force transmitters 19 act as a web tension-sensing device which is operatively connected to the web W and which generates a tension signal 21 and each such signal is fed through suitable conductors to the web tension controller 30. The controller 30, in turn, provides a controller output 31 that is a function of tension in the web W.

A set point signal 24 from a pressure regulator is indicated as desired film tension on the operator's gauge 23, and applied as the set point input to the controller means 30. The con troller output 31 is proportional to the error.

The controller output 31 is fed through suitable conductors to a transducer 32 which converts the pneumatic controller output 31 to a mechanical output. The transducer 32, in turn, is suitably connected to a variable transformer 33 as is known in the art for converting the mechanical output from the transducer 32 into an electrical output in the form of a control signal 34. Tension above the set point causes the control voltage or signal 34 to be lowered. Tension above the set point causes the control voltage or signal 34 to be raised.

FIG. 5 is a schematic representation of the electrical system of this invention and shows the control voltage or signal 34 from the transformer 33 being applied to the control circuit.

Rectified DC current 35 from the transformer 33 increases when the control voltage 34 is increased, and decreases when the control voltage 34 is decreased. It follows that the magnitude of the control current 35is automatically increased whenever the web tension level is below the set point level, and is decreased whenever the tension goes above the set point 24.

. The main components in the electrical portion or section of the control system are first and second magnetic amplifiers 40 and 41.

The first magnetic amplifier 40 controls the first windup roll 10 and consists of four windings; one control winding 42 in the control circuit, and three windings 43, 44, and 45 in the armature circuit of the first windup roll 10. The windings 43 and 44 are a variable inductance in the alternating current circuit supplying the power to the armature A-l of the first windup roll 10. The windings 43 and 44 are a variable inductance in the alternating current circuit supplying the power to the armature A-1 of the first windup roll 10. The magnitude of the direct current passing through the control winding 42 and the feedback winding 45 determines the magnitude of the inductive reactance produced within the two controlled windings 43 and 44. Increased current through the control winding 42 decreases the impedance to current flow through the controlled windings 43 and 44 and, therefore, increases the current 46 flowing through the armature A-l of the first motor M-l. Increased current through the negative feedback winding 45 increases the impedance to current flow through the controlled windings 43 and 44 and, therefore, decreases the current 46 flowing through the first motor M-l armature A-l.

The second magnetic amplifier 41 controls the second windup roll 20. This magnetic amplifier 41 is identical in function to the first magnetic amplifier 40 with a control winding 47, a feedback winding 48, and two controlled windings 49 and 50 for controlling the current supplied to the armature A-2 of the second DC motor M-2 which, in turn, drives the second windup roll 20.

When winding at a constant tension with a typical shunt wound direct current motor, the armature current must be increased directly with the roll buildup of the windup roll. When the web being wound is supplied at a constant line speed, the motor r.p.m. must decrease as the roll diameter increases. It is characteristic of a direct current motor that the armature current (and hence the torque) will increase as the speed of the motor decreases. The tension control circuit will provide the proper control current 35 to maintain constant tension irrespective of these characteristics; however, the speed at which the second windup roll 20 not then the winding the web of film, runs is very important to a successful web transfer. The speed is determined directly by its applied armature voltage. In practice the voltage being supplied, to the armature A-ll of the first windup roll 10 winding film, by the action of the control system is dropping as the diameter of the roll increases. If this same voltage was applied to the armature of the empty second windup roll 20, it would turn too slowly to pick up the web during a transfer from the first windup roll 10.

The same control current 35 flows through the control winding 42 for the first magnetic amplifier 40, and the control winding 47 for the second magnetic amplifier 41 but the currents through the negative feedback windings 45 and 48 are proportional to the load on the windup rolls 10 and 20. As film builds upon the first windup roll 10, and the armature current increases; the current through the negative feedback winding 45 will increase. The resulting increase in the impedance of windings 43 and 44 will tend to lower the armature current 46 to the armature A-l of the first motor M-1, and, hence, the torque. The decrease in torque will be sensed as a drop in tension and the control system will cause the control current 35 to increase. In practice, increasing the value of a resistor 51 in parallel with the winding 45 will cause a higher percentage of the armature current 46 to flow through the winding and thereby cause the control current to increase more rapidly as the windup roll 10 builds up.

The unloaded second windup roll 20 is subject to an armature voltage which is proportional to the control current 35 because the unloaded roll 20 runs at no load current which is independent of the armature voltage. Proper adjustment of the resistor 51 will prevent the control current from dropping and can be made to provide a good film or web transfer form one windup roll to the other.

The second windup roll 20 operates in a corresponding fashion with its armature current 52 being divided between the negative feedback winding 48 and a resistor 53.

As to stopping and starting, the first windup roll will run when its contractor 60 is energized, which action closes its contact 61 in the armature circuit and opens its contact 62 in the dynamic braking circuit. Deenergizing the contactor 60 opens contact 61 and closes contact 62 which allows current generated by the motor M-l to cause dynamic braking action. The diode 63 prevents braking action when the windup roll 10 is manually turned in the reverse direction.

The second windup roll 20 operates in a corresponding fashion through the action of its contactor 70, contacts 71 and 72 and diode 73. The resistors 74 and 75 serve to limit the current and, thus, the braking action.

After the desired amount of web material has been wound onto the core 16 of the first windup roll 10, the leading edge of the remaining web of material is transferred onto the empty core of the windup roll 20, as the windup roll 20 rotates to wind the web thereon in the manner shown in US. Pat. No. 3,157,37 l to Billingsley et al. for example.

After transfer is completed, the new windup roll 20 is permitted to build up to the desired diameter using the previously described technique. In the meantime, the wound roll is removed from the inactive windup roll 10 and'a new core is mounted thereon in preparation for the next transfer.

The winding operation of this invention permits continuous winding of a web of material while providing substantially constant tension on the web being wound throughout the winding operation in a novel manner as will be seen from the following description.

OPERATION In the operation of an apparatus of this invention, the web W is advanced under and over the various transfer rolls 11- -15 and onto the core 16 of the first windup roll 10 where it is wound into roll form.

The first windup roll 10 is driven by the first motor M-1 and the rotational speed of the core 16 is controlled through controller 30 by the tension on the web W as determined by the force transmitters 19 which are operatively positioned adjacent the tension roll 12. Power is delivered to the motor M-l upon actuation of a start switch S. Motor M-l operates at variable speeds and is energized from the power line, as depicted in FIG. 5, which is connected to a main power switch (not shown).

When the measured film or web tension, from the force transmitters 19 does not match the preset tension when on the operator's gauge 23 compared by the web tension controller means 30, the controller means 30 effects an increase in voltage with a corresponding current increase in the magnetic amplifier control circuits. The voltage is continually increasing at the tension control variable transformer 34 from startup to final roll diameter. Since the magnetic amplifier control circuits C-1 and C-2 of each windup roll 10 and are connected in series. the current in the control winding 42 of the first windup roll 10 will be the same as the current in the control winding 47 of the second windup roll 20. Correspondingly, the field voltages for each of the DC motors M-1 and M-2 is from a common constantsupply; therefore, there will be the same effect in voltage at the armatures A-1 and A-2 of the windup rolls 10 and 20 due to the tension control signal.

With an increase in voltage applied to the magnetic amplifier control windings 42 and 47 in the control circuit, there tends to be a corresponding increase in the applied armature voltage of the windup rolls 10 and 20; but, since the first windup roll 10 cannot go faster than the preset line speed of the web W, the torque developed by the first motor M-l increases with an attendant increase in armature current. Thus, with the closed-loop constant tension control system, the measured film tension senses an increase in effective tension to the predetermined set-point.

In each armature circuit -A-1 and A-2, there is a fixed resistance 51 and 53 placed in parallel with each magnetic amplifier feedback windings 45 and 48. Current through these windings 45 and 48 opposes the effect of the current through the control windings 42 and 47 (it creates a decrease in voltage in the magnetic amplifier armature circuits). The parallel combination of the fixed resistors 51', 53 and magnetic amplifier. windings 45, 48 constitute a current divider. Thus, a fixed percentage of the armature current passes through the feedback winding 45, 48; and higher armature current causes a decrease in voltage in each magnetic amplifier armature circuit. Since the speed of the motors M4 and M2 decreases as the armature voltage decreases, the higher the percentage of the total armature current that passes through the magnetic amplifier winding the more likely it is that the film tension will tend to decrease. Since the controller means 30 senses a decrease, the control circuit with the sequential corresponding interaction in the armature assures that the effective applied armature voltage to the second motor M-2 of the unloaded second windup roll will be higher than the applied armature voltage to the first motor M-l of the loaded first windup roll.

By proper sizing of the parallel resistors 51 and 53, the system can be tuned so that the unloaded windup roll 20 is neither too slow nor too fast for a satisfactory film transfer, i.e., a speed that gives a very slight, short-lived, increase in the film tension.

The tension force transmitters l9 measure the total force of web W of film on the tension roll 12, as best seen in FIG. I, and this is compared with the predetermined set-point by the controller means 30.

The single pneumatic tension control circuit operates a variable output transforrner 33 which, in turn, determines the magnitude of the DC current through the control windings 42 and 47 of the respective first and second magnetic amplifiers 40 and 41.

The control winding 42 for the first magnetic amplifier 40 of the first windup roll 10 is in series with the control winding 47 for the second magnetic amplifier 41 of the second windup roll 20. The control current through the respective magnetic amplifiers is identical. Increased current through the control windings 42 and 47 tends to increase the voltage output of each magnetic amplifier 40 and 41.

The voltage output of each magnetic amplifier 40 and 41 is the applied armature voltage to each of the first and second DC motors M-l and M-2 which the respective magnetic amplifiers 40 and 41 control.

By increasing the applied armature voltage, the motor torque increases. The torque developed by a DC motor is directly proportional to its armature current. The torque will increase as the windup roll slows down. Therefore, the DC motors torque is directly proportional to the applied armature voltage of its magnetic amplifier and inversely proportional to its speed.

Theoretically, constant film tension can be maintained if the motor torque is increased hyperbolically as the speed of the windup roll decreases. As a practical matter, other variables, such as friction, may alter this slightly.

It should be recognized, importantly, when winding with a DC motor, that if the applied armature voltage is held constant, the torque developed by the motor will increase linearly as the roll slows down. Theoretically, constant tension winding may be accomplished by selective use of any of several systems, such as e.g., direct measurement of the diameter of the windup roll, measurement of the speed of the windup roll and line speed to pattern the current or applied voltage, or measure the horsepower output of the motor to hold it constant.

The tension feedback control system provides the exact applied armature voltage necessary to maintain the predetermined constant tension while the roll increases in diameter.

In order to transfer the moving web W to the unloaded second windup roll 20, the speed of the windup roll 20 should be greater than the line speed of the web W, preferably by about 10 percent greater. As indicated before, the speed of a DC motor is directly proportional to the applied armature voltage; hence, the motor M-2 must receive this increase in applied armature voltage.

If the applied armature voltage is the same to each DC motor M-l and M-2 driving the windup rolls l and 20 and since the applied armature voltage must decrease as the roll diameter on the first windup roll increases to its maximum diameter, the decreasing applied armature voltage would cause the unloaded second windup roll 20 to rotate at a speed less than line speed of the web W. This would cause the film to go slack and, thus, cause an unsuccessful roll start after transfer.

when simultaneously controlling both windup rolls l0 and 20 from a tension feedback signal, the control system should provide for the no-load windup roll 20 to run at a speed faster than the film or web W line speed. Therefore, the control system provides an applied armature voltage 52 to the second DC motor M-2 of the unloaded second windup roll 20 greater than (about 10 percent greater) the applied armature voltage 46 to the first DC motor M-l of the loaded windup roll 10.

In the armature circuit A-1 and A-2, there is a magnetic amplifier 40 and 41 for each DC motor M1 and M-2. The voltage at the output of each magnetic amplifier 40 and 41 is the applied armature voltage to the DC motor M-l and M-2 it controls. Each magnetic amplifier 40 and 41 has a feedback winding 45 and 48 which opposes its control winding 42 and 47. The feedback current tends to reduce the voltage mea sured at the output of the magnetic amplifiers, and the apparent resultant drop in film tension causes the controller means 30 to increase the tension control signal. The tension control signal 34 is applied equally to both of the magnetic amplifiers 40 and 41. The actual applied armature voltage 46 and 52 is the result of the action of the tension control signal minus the action of the feedback signal.

As the diameter of the web being wound onto the first windup roll 10 increases, a linear increase in torque is required to maintain the constant tension preset and the armature current 46 is increased by the tension control signal. The applied armature voltage 52 to the unloaded windup roll 20 increases because of the increased tension control signal. Since there is no load on the unloaded second windup roll 20, its armature current 52 results in a very low feedback.

Thus, since the speed of a DC motor is directly proportional to the applied armature voltage, the applied armature voltage 56 of the unloaded windup roll 20 and, thus, its speed will always be greater than the applied armature voltage 46 of the loaded windup roll 10 and its corresponding speed. As a result, the speed of the unloaded windup roll 20 will be greater than the film line speed at time of web transfer from the first windup roll 10 to the second windup roll 20.

Obviously, as soon as the roll transfer has taken place the web constant tension system senses and establishes the required tension, voltage current, control; as is known in the art having received assurance from the apparatus of this invention that the web tension will automatically and accurately be that which is both sought and desired.

lclaim:

1. Apparatus for winding a web of material comprising:

a first windup roll adapted to be driven by a first DC motor;

a second windup roll adapted to be driven by a second DC motor;

a web tension-sensing means operatively connected to the web;

a web tension controller means operatively connected to the web tension-sensing means and adapted to transmit motive power to the first and second DC motors responsive to a control signal from the web tension-sensing means; and,

the web tension controller means adapted to generate a response proportional to a feedback signal from the respective first and second DC motors.

2. The apparatus of claim 1 wherein the first and second windup rolls are mounted on a turret and means to transfer the empty second windup roll into the original position of the loaded first windup roll wherein the web is wound onto the second windup roll.

3. The apparatus of claim 1 including means for maintaining the applied armature voltage to the second DC motor driving the empty second windup roll greater than the applied armature voltage to the first DC motor driving the loaded first windup roll thereby to maintain constant tension during transfer of the web from the first windup roll to the second windup roll. 4. A method of winding a web of material onto successive windup rolls mounted on a turret including the steps of:

winding the web onto a first windup roll; transferring the web from the loaded first windup roll to an empty second windup roll; winding the web onto the second windup roll; sensing the tension on the web with tension-sensing means as it is wound onto the first windup roll; driving the first and second windup rolls; controlling the speed of the first and second windup rolls by means of signals from the tension-sensing means; and, wherein, the empty second windup roll is driven at a speed greater than the speed of the loaded first windup roll. 

1. Apparatus for winding a web of material comprising: a first windup roll adapted to be driven by a first DC motor; a second windup roll adapted to be driven by a second DC motor; a web tension-sensing means operatively connected to the web; a web tension controller means operatively connected to the web tension-sensing means and adapted to transmit motive power to the first and second DC motors responsive to a control signal from the web tension-sensing means; and, the web tension controller means adapted to generate a response proportional to a feedback signal from the respective first and second DC motors.
 2. The apparatus of claim 1 wherein the first and second windup rolls are mounted on a turret and means to transfer the empty second windup roll into the original position of the loaded first windup roll wherein the web is wound onto the second windup roll.
 3. The apparatus of claim 1 including means for maintaining the applied armature voltage to the second DC motor driving the empty second windup roll greater than the applied armature voltage to the first DC motor driving the loaded first windup roll thereby to maintain constant tension during transfer of the web from the first windup roll to the second windup roll.
 4. A method of winding a web of material onto successive windup rolls mounted on a turret including the steps of: winding the web onto a first windup roll; transferring the web from the loaded first windup roll to an empty second windup roll; winding the web onto the second windup roll; sensing the tension on the web with tension-sensing means as it is wound onto the first windup roll; driving the first and second windup rolls; controlling the speed of the first and second windup rolls by means of signals from the tension-sensing means; and, wherein, the empty second windup roll is driven at a speed greater than the speed of the loaded first windup roll. 